首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   205830篇
  免费   13652篇
  国内免费   1001篇
林业   23303篇
农学   14736篇
基础科学   3212篇
  39932篇
综合类   12182篇
农作物   16868篇
水产渔业   15466篇
畜牧兽医   66081篇
园艺   6290篇
植物保护   22413篇
  2021年   2420篇
  2020年   2875篇
  2019年   3633篇
  2018年   3660篇
  2017年   4048篇
  2016年   4691篇
  2015年   4281篇
  2014年   5610篇
  2013年   16150篇
  2012年   4829篇
  2011年   6762篇
  2010年   6999篇
  2009年   7710篇
  2008年   5922篇
  2007年   4847篇
  2006年   5787篇
  2005年   4995篇
  2004年   5009篇
  2003年   4696篇
  2002年   3939篇
  2001年   3963篇
  2000年   3640篇
  1999年   3945篇
  1998年   4040篇
  1997年   4134篇
  1996年   3833篇
  1995年   4402篇
  1994年   3768篇
  1993年   3694篇
  1992年   3306篇
  1991年   3370篇
  1990年   2924篇
  1989年   2918篇
  1988年   2490篇
  1987年   2535篇
  1986年   2401篇
  1985年   2819篇
  1984年   2823篇
  1983年   2756篇
  1982年   2479篇
  1981年   2449篇
  1980年   2451篇
  1979年   2350篇
  1978年   2253篇
  1977年   2169篇
  1976年   2014篇
  1975年   1757篇
  1974年   1755篇
  1973年   1693篇
  1971年   1438篇
排序方式: 共有10000条查询结果,搜索用时 562 毫秒
61.
62.
Landscape Ecology - The effects of changing land use, and especially urbanisation, on species and functional diversity are of global concern. Eco-estates are a form of urban housing development...  相似文献   
63.
A new cytotoxic thiodepsipeptide, verrucosamide (1), was isolated along with the known, related cyclic peptide thiocoraline, from the extract of a marine-derived actinomycete, a Verrucosispora sp., our strain CNX-026. The new peptide, which is composed of two rare seven-membered 1,4-thiazepane rings, was elucidated by a combination of spectral methods and the absolute configuration was determined by a single X-ray diffraction study. Verrucosamide (1) showed moderate cytotoxicity and selectivity in the NCI 60 cell line bioassay. The most susceptible cell lines were MDA-MB-468 breast carcinoma with an LD50 of 1.26 µM, and COLO 205 colon adenocarcinoma with an LD50 of 1.4 µM. Also isolated along with verrucosamide were three small 3-hydroxy(alkoxy)-quinaldic acid derivatives that appear to be products of the same biosynthetic pathway.  相似文献   
64.
65.
Osteomyelitis caused by Cryptococcus neoformans was diagnosed in a three-year-old male Irish wolfhound. The case details and radiological findings of radiolucency and periosteal reaction of the left third metatarsal bone had lead to an initial diagnosis of a malignant bone tumour. Biopsy revealed a fungal granuloma and culture identified the causal organism. A four month course of ketaconazole was instigated and the lameness resolved. Twelve months after the end of treatment there was no recurrence of the problem.  相似文献   
66.
67.
Differences in gas exchange parameters i.e. carbon exchange rate (CER), transpiration (Tr), water vapor conductance (g) were investigated, under a controlled environment, in a semi-dwarf (SD) Triticum aestivum line, its tall (TL) near isoline and the Payne (PA) variety characterized by small leaves. The plants were maintained in: (a) optimal substrate moisture condition (CTR); (b) salinized by watering with a 0.12 m NaCl solution (SLT); (c) water stressed by withholding waterings during a period of six days (STR); (d) stressed and salinized during the same period and with the same saline solution (S + S). CER and Tr were negatively affected by the stresses; SLT and S + S treatments had a higher WUE compared to their respective controls CTR and STR.
SD line had a better performance in terms of CER and WUE, particularly when water and salt stresses interacted. Leaf anatomy and assimilation/internal CO2 concentration curves contributed to explaining the SD performance.  相似文献   
68.
69.
Abstract. A humoral antibody response was demonstrated by ELISA in rainbow trout immunized intraperitoneally with extracts from the branchiuran ectoparasite Argulus foliaceus. A similar immunization protocol produced a higher titre response in a rabbit. Both trout and rabbit identified several antigenic components on immunoblots. ELISA and immunoblotting indicated that rainbow trout and rabbit anti-A. foliaceus sera identified components from the parasitic copepods Lepeophtheirus salmonis and Caligus elongatus.  相似文献   
70.
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号